1. Field of Invention
The invention relates to an electromagnetically driven valve control apparatus and method.
2. Description of Related Art
Control apparatus for electromagnetically driven valves adopted as intake valves or exhaust valves of internal combustion engines have been proposed. See, e.g., Japanese Patent Application Laid-Open Publication Nos. 2001-207875, 2000-234534, 2001-221022, and 2001-221360. Such control apparatus perform a position control of a movable element so as to achieve a target operation characteristic, for example, a control of changing the velocity of the movable element, or reducing the velocity of the movable element close to “0” at the time of reaching a seated position, or causing the movable element not to reach a seated position when the internal combustion engine is in a specified operation region, in order to reduce the impact noise produced by the movable element.
In conjunction with these technologies, a technology has been proposed in which an electromagnetically driven valve is modeled as a spring-mass vibration system in order to achieve a target operation characteristic as mentioned above. The value of electric current output to electromagnets in order to achieve a target operation characteristic is adjusted on the basis of a physical model in which the mass of the movable portion, the spring constant and the viscosity coefficient are used as model parameters.
In the aforementioned technology, an electromagnetically driven valve control is executed with the model parameters, that is, the mass of the movable element, the spring constant and the viscosity coefficient, being fixed. The electromagnetically driven valve has a movable element that is driven by cooperation of spring force and electromagnetic force, and a valve body that is engageable with the movable element. The electromagnetically driven valve performs open-close actions in which the movable element engages with the valve body in accordance with the driving of the movable element. Therefore, there exist periods during which the movable element is moving in a state of disengagement from the valve body, in addition to the periods during which the movable element is moving in a state of engagement with the valve body.
In the above-described technology, the electromagnetically driven valve control is executed on the basis of the model with the fixed model parameters, assuming that the valve operates in the engaged state all the time while ignoring the period of operation in the disengaged state. Therefore, during the disengaged state operation period, the spring-mass vibration system model deviates from the actual spring-mass vibration system. For example, after the valve body is seated during movement of the movable element toward the closed valve side, the movable element separates from the valve body, so that the actual mass is only the mass of the movable element, and therefore, the actual spring constant is the spring constant of the spring that urges the movable element. Furthermore, the actual viscosity coefficient becomes the viscosity coefficient related to movement of only the movable element. Due to occurrence of such a deviation of the spring-mass vibration system model, the characteristic of electromagnetic force produced by the electromagnets does not correspond to the target operation characteristic, thus giving rise to a problem of degraded precision of the electromagnetically driven valve control.